Abstract:This paper addresses the design of a class of anticollision algorithms for passive RFID (radio frequency identification) systems, where tags are allowed to cooperate by relaying (if necessary) the signals of other tags towards the destination. All the relayed signals are combined at the reader side so as to improve tag detection probabilities. The work is focused on asymmetrical scenarios where tags and readers experience different channel statistics. The objective is to include tag cooperation in RFID anti-collision algorithms. To achieve this goal, a framework for medium-access-control and physical (MAC/PHY) cross-layer design of cooperative RFID anti-collision algorithms is here presented. A tag activity model is also proposed where different tag states are initially selected according to the tag activation SINR (signal-to-interference-plus-noise ratio). Tags activated by high SINR values enter into states with relaying capabilities, whereas those with low SINR values act as simple sources of information (non-relaying state). Tags can change state depending on the number of (re)transmissions performed. A Markov model is used to calculate the system steady-state probabilities. Instability is evaluated by the number of tags in the backlog state, while fairness is evaluated by means of the Gini index. Results show that tag cooperation is useful in networks where tags with good channel states and low traffic requests cooperate with tags with bad channel states and low traffic requests.